This invention relates generally to apparatus and methods for cutting an object in a well and more particularly, but not by way of limitation, to an apparatus and method for cutting a tubular element in a well with a combination of less sensitive and more sensitive explosives transported in small enough quantities to qualify as class C explosives but consolidated and assembled at a field location to provide an adequate explosive force to cut the tubular element.
Tubular elements, such as drill pipe or casing, or other objects located in an oil or gas well sometimes need to be cut or severed. One type of device for doing this is an explosive cutting tool. Such a tool includes an explosive which, after the tool has been lowered into the well to the location where the cut is to be made, is detonated to provide a cutting force.
Explosive cutting tools used to sever drill pipe, casing or other objects used in oil and gas wells require explosive charges greater than 22.7 grams, the weight limit above which an explosive is categorized as class A material. These large explosive loads impose special safety considerations, result in time delays and must be transported as class A material as defined by pertinent United States regulations. Having to transport such a cutting tool, or the explosive thereof, as class A material imposes additional shipping expense, particularly when the tool or explosive component is to be exported.
It would be desirable to provide an explosive cutting tool which could be shipped in a manner which qualifies for class C status (explosive less than 22.7 grams) because this would permit less expensive, more expediently dispatched transportation. Such a tool should, however, still be capable of use in a well to provide a sufficient explosive force to cut the object as desired.
Such a cutting tool, or the explosive charge of such tool, can be manufactured from a less sensitive material and divided into small shipping quantities to meet class C requirements; however, such less sensitive material alone typically lacks adequate detonation sensitivity, which poses detonation problems and can result in such a tool failing to make the desired cut.